The invention relates to a transformer and an associated production method.
High-frequency transformers for high output currents are predominantly planar constructions with stamped laminations for the secondary winding. The primary winding is usually likewise laminated or is also produced with stranded wire.
The correct electrical connection of the laminations to one another is associated with high outlay.
A further problem is the cooling of the component, since the heat loss of the windings has to be removed predominantly through a surrounding ferrite core. Ferrite material is a poor thermal conductor however, and a thermal connection over the entire surface on both sides to a heat sink is difficult to implement.
The implementation of the necessary insulation clearances without excessive enlargement of the leakage inductances is additionally problematic.
The object of the invention is to provide a transformer and an associated production method, which enable efficient cooling of the transformer with the lowest possible outlay.
The invention achieves this object by providing a transformer, and a production method therefor, for switched-mode power supplies. The transformer includes a magnetizable core having a winding axis, at least one primary winding, which is formed by a primary winding conductor that at least partly surrounds the winding axis of the core, and at least one secondary winding, which is formed by a secondary winding conductor. The secondary winding conductor surrounds the primary winding conductor, and is formed in one layer. A cross section of the secondary winding conductor is rectangular, in particular, square.
The transformer is preferably suitable or intended for switched-mode power supplies and has: a magnetic or magnetizable core, in particular a ferrite core, which defines a winding axis or has a winding axis, at least one primary winding, which is formed by a primary winding conductor, in particular in the form of a litz wire that is insulated a number of times, and which at least partly surrounds the winding axis of the core or a limb of the core, through which the winding axis runs, and at least one secondary winding, which is formed by a secondary winding conductor. The secondary winding conductor surrounds the primary winding conductor, that is to say the secondary winding conductor and the primary winding conductor form different winding layers over the winding axis. The secondary winding is formed in one layer, and a cross section of the secondary winding conductor is rectangular, in particular, square. Due to the cross section and the resultant outer contour, the secondary winding can be coupled very easily and with low thermal resistance to a cooling surface, for example. The cross section of the winding, which is solid in particular, or of the solid conductor, is intentionally overdimensioned here, such that an efficient heat flow is possible within the winding.
In an embodiment the secondary winding conductor is solid, that is to say the entire cross section of the conductor is filled with conductor material, or the conductor is filled completely with conductor material within its outer dimension. The conductor in particular is not constructed by interwoven stranded wires, by a plurality of combined individual conductors, or in the form of a hollow conductor or the like.
In an embodiment the at least one secondary winding is formed from a solid material block, which is structured to form the secondary winding conductor, in particular is structured by drilling, cutting and/or milling. Alternatively, the at least one secondary winding is formed from a diecast shaped article.
In an embodiment the transformer has a nominal output, wherein the (minimum) cross section of the secondary winding conductor is dimensioned in such a way that a current-carrying capacity of the secondary winding conductor is greater than is necessary for the nominal output, that is to say the cross section of the conductor is overdimensioned in relation to the nominal output.
In an embodiment the secondary winding conductor consists of copper or titanium, particularly preferably of aluminum.
In an embodiment a planar cooling element is provided, which is thermally coupled to the secondary winding, in particular to the side of the secondary winding facing away from the winding axis of the core. A heat-conductive electric insulator is preferably provided and is arranged between the cooling element and the secondary winding. The electric insulator is preferably an electrically insulating heat-conductive foil.
In accordance with the invention, the secondary winding or the secondary winding conductor forms a thermal bridge to the planar cooling element. Core losses and losses of the primary winding(s) pass initially to the secondary winding(s), for example in order to then be removed via the planar cooling element in the form of a water-cooled cooling plate.
In an embodiment the secondary winding forms a heat sink.
In an embodiment a distance between the primary winding and the core and a distance between the secondary winding and the primary winding are selected in such a way that leakages are minimized. In other words, the primary winding lies as tightly as possible over the core and the secondary winding lies as tightly as possible over the primary winding, such that there are minimal losses caused by leakage fields and good thermal coupling of the system is also achieved.
In the method for producing the above-mentioned transformer, the secondary winding is formed from a solid material block, which is structured to form the conductor, in particular as a result of material removing machining in the form of drilling, cutting and/or milling.
The invention will be described hereinafter with reference to the drawings, which illustrate preferred embodiments of the invention.